Auto White Balance (AWB) is the process of removing unrealistic color casts from captured images, so that objects that appear white when viewed directly by a human viewer are rendered white in the corrected images. Human vision system has the ability to adapt to changes in illumination in order to maintain the appearance of object colors, which is also called chromatic adaption. Digital cameras that perform AWB estimate the color property of an illuminant (a light source), similar to the chromatic adaptation of human vision system. The digital camera may alter captured image data based on the estimate of the illuminant to correct color artifacts that arise due to the illuminant color. Essentially, the AWB algorithms attempt to null out color casts that are imposed in the image due to the illuminant color, which would generate an image reflecting the image content's appearance, as seen by human vision system.
Estimation of the illuminant's characteristics from the camera's response can be difficult because it represents the integral of spectral distribution of the illuminant, reflectance of the object and camera spectral sensitivities. Derivation of illuminant characteristics from the camera response is challenging because the object colors and illuminant colors are mixed together. The inventors perceive a need in the art for a technique that better estimates characteristics of an illuminant in order to perform white balance corrections.